I own a dl 50 and a 111, also a crrc pro 50 and a crrc 26.
The Dls have always run like a dream and have needed no work after 3-400 odd flights between them.
The crrc are a very different matter, neither have ever been hand 'startable' the 50 never made it into the air, on the first few bench runs it ate the front main bearing damaging the piston,liner,front seal, it is not worth repairing and not worth sending back to China.
The 26 managed about fifty flights before the compression started to tail off. strip down revealed a chrome bore that could be scratched with a finger nail. If you gave me a crrc I would sell it, if I was not allowed to sell it, I would not fit it to an airframe.
Yes a four stroke would be the ideal mill for a cub, but not one of those silly glow things that spews oil all over your airframe and costs a fortune to buy and run.